High pressure stirling cycle engines



Oct. 15, 1968 D. A. KELLY HIGH PRESSURE STIRLING CYCLE ENGINES Filed Aug. l2. 1966 3 Sheets-Sheet 1 33 5/\3z\)42|: G- Z 9 6639 29 /5 /7 30 l v. viv/"6 (34 ///.37 ///////4///// l n QW "m-"` I mfr r. I m k I" I 2 Vm 2 l lI /'f/l 42 j j je@ fd r 2/ j 6 6 7 25 I \Z0 /9 4 /6 FIG. 1

INVENTOR.

Oct. 15, 1968 D. A. KELLY 3,405,521

HIGH PRESSURE STIRLING CYCLE ENGINES INV ENTOR.

M/aft@ D. A. KELLY HIGH PRESSURE STIRLING CYCLE ENGINES 3 Sheets-She@t 3 Filed Aug. 12y 1966 .n XE

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United States Patent O 3,405,521 HIGH PRESSURE STIRLING CYCLE ENGINES Donald A. Kelly, New York, N.Y. (5806 69th Place, Maspeth, N.Y. 11378) Filed Aug. 12, 1966, Ser. No. 572,130 6 Claims. (Cl. 60-24) ABSTRACT F THE DISCLOSURE The invention consists of a Stirling Cycle engine having dual coaxial pistons housed in separate in-line cylinders. The box-type displacer piston may be of variable size and provided with multiple ball bearings for low friction operation. The box displacer piston is fabricated with multiple sloped regeneration bores which are fitted with fine mesh filament. The displacer housing is constructed in three separate sections for thermal isolation and internally provided with multiple bellows-like metal strips for thermal saturation.

This invention relates to an improved type of externally heated, internally pressurized Stirling Cycle engine. The classic Stirling closed cycle is basically an externally lired heat engine in which a nearly constant volume of gas is alternately heated and cooled to produce a half power stroke and half pull stroke, on the power piston.

The conventional Stirling pressurized engines currently under development and in use consist of dual coaxial pistons, one displacer and one power piston reciprocating within a common cylinder. The approximate ninety degree phase angle at the crankshaft keys the cycle so that the displacer piston follows the power piston downward for the half power stroke, thereby allowing the expending gases to push effectively on the power piston. In a similar manner the displacer piston follows the power piston on the upward half pull stroke. The two pistons are in line and connected in phase to a common output shaft through linkage and gearing.

Since the conventional engine combines the cold clearance volume with the power piston volume a certain amount of thermal quenching occurs when the hot expanding gases contact the cold wall areas, with a corresponding loss of efficiency. A further unavoidable deficiency in the common cylinder arrangement is that the compression ratio is inherently set at a low value of about two or three to one. This low compression ratio leads to the application of an undesirable high internal pressure in order to produce competitive power-to-displacement ratios of about two horsepower per cubic inch of piston displacement.

The described invention attempts to circumvent certain of these problems, while striving to maintain a simple, produceable and economical engine no external regeneration ducting and a minimum of complexity. Design simplicity is enhanced by the adoption of a rectangular modular housing with the two different size in-line pistons connected to a common output shaft. A major factor in the engine simplicity and compactness is the use of internal regenerator bores within the displacer piston. The multiple bores are sloped to a common apex centered on the power piston centerline thereby providing a zone control in which the hot gas ow is directed away from the cold cylinder walls. The bores contain the regenerative filament of silver or copper wire. This type of internal regeneration system although not as eflicient as the conventional external ducted type due to the reduced surface area and fully displaced gas ow, is desirable for construction simplicity. The ineiciency of internal regeneration in this engine design is somewhat offset by the use of an oversize displacer piston which provides a greater differential gas volume between the solid piston Volume and its regenerator bores. To reduce friction the nearly square displacer piston is fitted with multiple ball bearings which are pinned to the displacer piston and roll along the inside of the displacer housing walls.

The present invention avoids the low compression ratio problem by providing separate in-line cylinder and housing sections of different internal volumes, thereby producing a slight net increase in displacer volume compared with power piston volume. This arrangement is a residual feature produced by the adoption of the rectangular displacer and housing which follows the modular housing concept, as previously stated.

A feature of the housing design is the splitting or division of the hot and cold sections in order to achieve a higher delta temperature between the hot and cold clearance volumes. This division is highly desirable since it precludes direct thermal transfer through the housing walls between the hot and cold sections.

Another innovation in this design is the application of thermal saturation strips in each of the clearance volumes, which provides a means of more fully heating and cooling the clearance volumes. The thermal strips must expand and retract in a bellows-like lmanner to provide for displacer piston movement. The strips must remain in contact with the interior housing walls for proper heat transfer from the walls to the strips in both clearance volumes. The smaller cold clearance thermal strips must remain outside of the hot gas ow eminating from the sloped regenerator bores, to minimize premature thermal quenching.

A feature of the design which contributes to the overall compactness of the engine is the application of a scotch yoke arrangement to convert the reciprocating displacer piston motion into rotary motion required at the crankshaft.

It is an object of the invention to provide an arrangement of a Stirling Cycle engine which will be simple and inexpensive to construct by adopting a modular concept, and to utilize a maximum number of stacked, standard components.

A second object of the invention is to use an internal regenerative arrangement consisting of multiple sloped bores containing filament for manufacturing simplicity and for thermal zone control.

A third object of the invention is to provide a simple rectangular displacer block larger than the power piston in order to achieve a higher compression ratio than possible in conventional cylinder designs.

A fourth object of the invention is to provide the displacer piston with ball bearings, and the power piston with dry lm lubrication in order to minimize friction and wear and increase overall running efliciency.

A fth object of the invention is to provide a split external housing in order to separate the hot and cold clearance volumes so that no heat transfer and thermal loss occurs in the housing walls between the two sections.

Another object of the invention is to increase thermal transfer within the hot and cold clearance volumes by utilizing conductive saturation strips connected to the internal housing walls which will aid thermal conduction and operating eiciency.

A further object of the invention is to provide in-line reciprocating motion for the displacer piston =by the application of a scotch yoke arrangement with dual displacer rods.

A final object of the invention is to utilize the lightest weight material possible consistent with pressure strength including the latest filament-Whisker technology when possible.

While this invention was been described with particular reference to the construction shown in the drawing and whilevariousV changes may be made in the detail construction, it shall be understood that such changes shall be within the spirit and scope of the present invention as defined by the appended claims.

`In the drawings:

FIG. I is side longitudinal section taken through the engine.

FIG. II is a top longitudinal section taken through the engine.

FIG. III is an end section taken through the displacer housing looking at the power cylinder.

FIG. VI is a schematic diagram showing the phasing arrangement for a more compact engine.

FIG. V is a pictorial view of the displacer and power piston relationship with connecting drive system.

FIG. VI'is a schematic diagram showing the phasing and timing of the engine cycle.

Referring to FIGS. I through VI it may be seen that the cylinder 1 contains the power piston 2 which is coupled to the connecting rod 9 by the wristpin 10 and cushioned by the Teon bushings 11. The connecting rod 9 `free end connects to the crankpin 12 which is press fitted into the crankdisc 18. The power cylinder 1 is mounted within the main housing 6 and offset to one side to allow for mounting of the output shaft bearings 21 and 24. The main housing 6 is built up of multiple at plates which are secured with machine screws 7 with all butting joints made high pressure tight with special sealing compound.

The displacer housing 3 is made up of multiple fiat plates built up to form two boxlike halves which are joined and made pressure tight by the reinforced Fiberglas insulation sleeve 4. The displacer housing assembly 3 is secured to the main housing 6 with the machine screws 7.

The displacer piston is coupled to the displacer link 13 by the yoke 17 and the two displacer rods 29. The displacer link carries the dis-placer pin 14 and the hall bearing 15 and is secured to the crankpin 12 by four machine screws 7. The ball bearing 15 moves up and down within the yoke slot 16 when the crankdisc 18 revolves and thereby imparts a reciprocating motion to the displacer piston as required. The position of the displacer link 13 is arranged so that the displacer pin 14 is about ninety degrees away from the crankpin 12 position for the phasing of the cycle. The engine rotational direction may be reversed by reversing the position of the displacer pin 14 by about one hundred eighty degrees. The crankdisc 18 is connected to the crankshaft 19 which is supported by one ball bearing 21 and flange 20 located inside the main housing 6. Another ball bearing 24 and mounting flange 22 are secured to the outside of the main housing 6 and support the output end of the crankshaft 19. A pressure seal 23- is located on the outside of the ball bearing 24 within the mounting flange 22. Both mounting anges and 22 are secured to the main housing by the machine screws 25 and 26 respectively. The support plate 27 positions and supports the power cylinder 1 and carries the ball bearing 21 and mounting ange 20. The separator plate 28 with the cylinder port 43 divides the main housing 6 cylinder area from the displacer housing 3 cold clearance area and positions and supports the power cylinder. The machine screws 8 secure the separator plate 28 in place in the main housing 6. The displacer piston 5 is fitted with twelve ball bearings 30 which are supported by twelve brackets 31 and twelve pins 32 and these assemblies are nested into the twelve slots 33.

Filled Teon piston rings 34 are fitted on the power piston 2. Power piston 2 is treated with a lubrication iodine film for dry running within the power cylinder for extended periods of time.

The multiple sloped regenerator bores 35 within the displacer piston 5 are arranged to converge into a single arc-.i

4 Y opening at the cold clearance side. At the hot clearance side the bore openings are equally spaced around "the perimeter of the displacer piston 5. This arrangement provides a converging gas ow so that the heated gas is isolated from the cold walls of the cold clearance volume of the displacer housing 3. v

The regenerator bores 35 are fitted with 4heat storage filament of copper or silver 36 which tendto retain the heat when the hot expanding gas flows through the displacer piston 5 going from the hot side to the working volume.

Additional ball bearings 37 are mounted on the power cylinder 1 with the blocks 38 and pins 39. These bearings 37 act as guides and supports for the reciprocating displacer rods 29 at the yoke 17 end of the drive.

Machine screws 40 lock the displacer rods 29 tothe yoke 17 and provide for length adjustment ofthe rods 29.

The crankdisc 18 is litted with a counterbalance crescent 41 which provides for exact dynamic balance of the drive system in operation and which is secured to the crankdisc 18 by the machine screws 25. The thermal saturation strips 42 for the hot and cold zones are fastened at one end of the inside displacer housing walls 3, and serve to more fully transfer Aheat uniformly in the hot and cold clearance volumes. The thermal strips 42 are made from a continuous sheet of lthin half-hard brass and uniformly folded to expand and contract in a bellows-like manner when following the reciprocating motion of the displacer piston 5.

In operation the fixed gas .volume is alternately heated and cooled in the displacer housing 3 hot and cold zones respectively. An effective design requires that a regenerative system be placed in the flow path between the hot and cold zones, either externally through ducting or as in this design through bores 35 in the displacer piston 5. Part of the heat of the expanding gases flowing from the hot zone is taken u-p by the regenerative filament 36. During the return ow the cooled gases from the cold zone take up this stored heat, which results in less heat getting lost through cooling for the working cycle. This function of regeneration effectively increases the power output of the engine and in this design is economically attained.

The key to the effectiveness of the thermal saturation strips 42 is their thinness and large surface area and therefore small volume relative to the volumes of the hot and cold clearance zones. The main function of the thermal strips 42 is to more rapidly heat and cool the medium within the natural time allowed by the cycle halves.

An alternate arrangement for the regenerator bores within the displacer is to increase their length by offsetting and thereby form multiple Z paths. The ends of the blind machined cross bores would be plugged to make machining feasible and economical. This arrangement would effectively increase the gas ow path through the regenerative area. The regenerator bores may also be slightly tapered to increase the flow velocity from the hot side to the power piston. Another arrangement for the regenerative elements 36 within the bores would be the application of thin, continuous copper or silver strips arranged to interlock and set equally spaced and thereby form multiple, longitudinal ow paths through the regenerator bores. This method would allow relatively large heat transfer surface areas without restricting the gas iiow through the bores.

A method of varying the hot and cold clearance volumes would -be the application of metal filler plates 43 which would be fitted to either or both ends of the displacer and therefore .provide a way to alter vthe operating characteristic of the engine and provide for optimizing the power output. The addition of ller plates 43 will require that the displacer stroke must be reduced to maintain the required fixed displacer end clearance. This adjustment is made by rotating and resetting the displacer link 13 about the crankpin 12, T-he thermal saturation strips 42 will be affected by the reduced volume but since they are flexible they will not detract from normal engine operation. This valve can be quickly reset once the overpressure is relieved so that the engine may.' again be put in operation.

Engine units may be ganged together to provide an increase in power output for many additional applications. The engine units can be stacked vertically with crankshafts geared or chained together, or the crankshafts may be connected internally through a special housing with a large common shaft emerging from the housing.

In the alternate arrangement of the engine the basic components are the same as that of the basic or first engine, except that the use of a single modular housing allows a somewhat simpler design.

T-he main housing 6 and displacer housing 3 are identical in cross-section and are joined by the insulation sleeve 4. The plate construction of the housings 6 and 3 are identical to that of the basic engine design. The piston plate 9', integral with the piston 2' takes place of the connecting rod, wrist pin and bushing of the basic engine design. The crankdisc 18 is placed as closely as possible to the power cylinder 1' to provide overall engine compactness. Other primed reference numerals correspond to the unprimed reference numerals used in FIGURES 1 and 2.

Some internal support plates and bulk-heads are eliminated in the alternate engine design due to the combining and redesign of certain components.

The functioning and performance of either engine arrangement would be identical since the operating merit -of the cycle is based on piston displacement, working pressure and thermal differential level.

It is recognized that the adoption of several design features of the described invention reduce the engine operating characteristics somewhat below Carnot efficiency but this is done to gain reasonable producibility. The degrading of the regeneration system contributes the greater of these losses and thus affects the work area of the P.V. diagram.

What I claim is:

1. A dense gas, closed Stirling Cycle engine comprising a cylinder, a piston in said cylinder, a main housing for containing the said cylinder, a crankshaft, means to support said crankshaft in bearings in said main housing, and means including a crank disc to connect said piston to said crankshaft to cause said crankshaft to revolve continuously while said piston reciprocates in said cylinder, a second housing, made in three sections the center section of which insulates one hot section and one cold section from each other, and means to heat said hot section and means to cool said cold section of said second housing, a box displacer in said second section housing connected to said crankshaft by two connecting rods Y which are attached to a scotch yoke at the opposite end of said connecting rods, an arm connected to said crank disc by a crank pin, and a displacer pin on said arm and which engages a slot in said scotch yoke thereby causing the said box displacer to reciprocate one-half stroke out of phase in the said piston, means to connect said second housing to said main housing so that the said box displacer lines up with said piston means, a plurality of regenerator bores within said box displacer which are sloped to converge at a common opening at one end of said box displacer.

2. A dense gas, closed Stirling Cycle engine according to claim 1, in which the said regenerator bores within said box displacer are increased in length by offsetting and thereby form a plurality of Z paths within said box displacer.

3. A dense gas, closed Stirling Cycle engine according to claim 1 in which the said box displacer is fitted with a plurality of ball bearings on its outer edges.

4. A dense gas, closed Stirling Cycle engine comprising a cylinder, a piston in said cylinder, a main housing for containing the said cylinder, a crankshaft, means to support said crankshaft in bearings in said main housing, and means to cause said crankshaft t-o revolve continuously while said piston reciprocates in said cylinder, a second housing made in three sections the center section o-f which insulates one hot and one -cold section from each other, a plurality of thin metal strips folded in a bellows-like manner and fastened to the interior ends of the said hot and cold sections, a box displacer in said second housing connected to said crankshaft by two connecting rods which are attached to a scotch yoke at the opposite end of said connecting rods, an arm connected to said crankshaft by a crank pin, a displacer pin on said arm and which engages a slot in said scotch yoke thereby causing the said box displacer to reciprocate one-half stroke out of phase with said piston, means to connect said second housing to said main housing so that the said box displacer lines up with said piston, a plurality of regenerator bores within said box displacer which are sloped so as to converge at a com-mon opening at the cold end of the said box displacer.

5. A dense gas, closed Stirling Cycle engine according t-o claim 4 and filler plates attached to said box displacer in order to reduce the volumes of the hot and cold sections, means for varying the stroke of the said box displacer to compensate for the addition of said filler plates.

6. A dense gas, closed Stirling Cycle engine according to claim 4 and a plurality of tapered regenerator bores in said box displacer arranged so that the large diameter ends are toward the said hot section, regenerative elements consisting of multiple thin tapered metal strips which interlock to hold theiry relative position within said tapered regenerator bores.

References Cited UNITED STATES PATENTS CARROLL B. DORITY, IR., Primary Examiner. 

